Biomechanics Notes PDF

Exam December 2, 2024 2:02 AM Compare the composition of ligaments, tendons, cartilage, and meniscus and their functions: Ligaments Tendons...

Exam December 2, 2024 2:02 AM Compare the composition of ligaments, tendons, cartilage, and meniscus and their functions: Ligaments Tendons Hyaline Cartilage Meniscus Bone Intervertebral Disc Muscle Structure The ECM: The ECM matrix: Locations: ears, nose, sternum, etc. Hierarchy structure: Cell type: fibroblasts Cell type: fibroblasts Hypocellular Hypocellular Primary focus: in articulating joints (diarthrodial). Hypovascular Hypovascular Mechanical purpose: cells and blood vessels are seen Mechanical purpose: cells and blood vessels are seen The ECM: as defects because they disrupt the uniform, load- as defects because they disrupt the uniform, load- Hypocellular (low amount of cells) and avascular (no blood vessels bearing structure. bearing structure. ○ Implication: poor repair Healing response: Healing response: Cell type: chondrocyte - live in a low-nutrient and hypoxic environment - Change in ao Very low due to less cells + vasculature Very low due to less cells and vasculature Hierarchical structure of hyaline cartilage: - Loss of elasti Involves reparative scar tissue Involves reparative scar tissue 1. Nano: type II collagen and proteoglycans (10-10 to 10-9) - Cyclic loading Poorly organized ECM after being injured Poorly organized ECM after being injured 2. Ultra: molecular organization (10-8 to 10-6) Function of muscles: 1. Tropocollagen (1.5 nm) 1. Tropocollagen (1.5 nm) 3. Micro: four zones of cartilage (10-7 to 10-4) - The engines of the muscle 2. Microfibril (3.5 nm) 2. Microfibril (3.5 nm) ○ Organization and concentration of proteoglycan and collagen by layer - Enable capacity for motion 3. Subfibril (10-20 nm) 3. Subfibril (10-20 nm) in cartilage - Provide stability (ex: spine) 4. Fibril: banding structure occurs (50-500 nm) 4. Fibril: banding structure occurs (50-500 nm) 4. Tissue: cartilage tissue (10-4 to 10-2) 5. Fascicle (elastin and collagen fibres): crimp occurs 5. Fascicle (elastin and collagen fibres): crimp occurs Cell: myocyte = muscle cell = muscle fiber (5-30 µm) (5-30 µm) 6. Ligament / tendon 6. Ligament / tendon Stress (σ) = Force / Area: When a force is applied to a smaller contact area, the resulting stress is higher. Conversely, increasing the contact area reduces stress by distributing the same force over a larger surface. Meniscus Function in the Knee Joint: The meniscus acts as a load distributor of the femoral condyles across the tibial plateau It increases the contact area between the femur and the tibia. ⚫ The nucleus pulposus carries compressive load through the centre of the disc - Pressures generate By spreading the load over a larger area, the meniscus ○ About 1.5 x the axial load on the spine - Blood pressure det - Contains additional organelles significantly reduces stress on the articular cartilage. ⚫ The compressive pressure on the nucleus causes outward pressure on the - Multiple nuclei pressure measured anulus fibrosus - Numerous mitochondria (energy production) - Blood pressure: sys Four Zones of cartilage at the Micro Level: ⚫ The anulus carries the load through the hoop stress (circumferential loading) - Very long, spindle-shaped cells that are up to 30 cm long! 1. Superficial zone: ○ The circumferential load is about 5x the axial load due to the hoop stress ○ Furthest from the subchondral bone effect 3 types of muscle: ○ Collagen fibrils are aligned parallel to the surface ▪ To help absorb and distribute shear stress 1) Skeletal muscle: ○ Chondrocytes are small and evenly distributed a. 40-45% of total BW ○ Has a greater modulus than the middle zone b. Attached to bones c. Voluntary control 2. Middle zone: ○ Collagen fibrils form arcades (arches) to transfer shear stress from 2) Smooth muscle: a. Surrounding vessels surface zone into tensile stress in the deeper zones. ○ "Arching arrangements of collagen fibrils" b. Gastrointestinal organs ○ Also hold proteoglycans in place c. Involuntary Inner: 2/3rd ○ Dense columnar arrangement of chondrocytes 3) Cardiac muscle: White region a. Heart 3. Deep zone: Avascular ○ Collagen fibrils oriented "vertically" (perpendicular to the surface) b. Involuntary Chondrocyte-like cells ▪ Secure into calcified bone Greater compressive load ▪ To provide strength and stability under pressure ○ Chondrocytes continue columnar but are less dense Outer: 1/3rd 4. Calcified zone: "transition into subchondral bone" Red region ○ Calcification of cartilage-transition between cartilage and bone Vascularized - Principal stresses influence how bone forms ○ Top surface is the "tide mark" Fibroblast-like cells ○ Vascular invasion when there's OA: ○ These cells are involved in the production of collagen fibers that help maintain the structural integrity of Advancement of the tidemark meaning: the cartilage. The fibroblast-like cells in this region The thickness of the calcified zone of cartilage is greater than normal play a major role in fibrous tissue repair and the formation of a collagenous matrix, which is essential for resisting circumferential load (stress applied around the joint). Bears circumferential load Collagen 75-80 (Type 1) 75-85 (Type 1) 50-75 (Type 2) Composed of Type 1 collagen Composed of Type 1 collagen [dry weight %] Collagen prevents the proteoglycans from swelling too much from the water they attract. Anulus fibrosus: holds in nucleus pulposus' pressure in the form of hoop stress Provides Without the structural support of Type II collagen, the proteoglycans would Ringed structure that surrounds the nucleus pulposus structure and expand excessively, disrupting the mechanical properties of cartilage. Lamellar structure with sheets of collagen fibrils arranged in alternating rigidity to the orientation with an interlamellar angle of 30 degrees tissue. Crimp pattern like tendons and ligaments: prevents crack propagation The anulus fibrosus experiences a pressure that is trying to push it outwards, however it resists this outward force and the loading develops in the wall of the anulus fibrosus (gets cycled) This prevents herniation of the nucleus pulposus and maintains disc stability Collagen fibers are arranged in a parallel, Collagen fibers are arranged in a parallel, Collagen is arranged circumferentially crimped pattern. crimped pattern. Helps to bear the hoop stress that is generated by the The straightening of this crimp under tension The straightening of this crimp under tension loading between the femoral condyles on the tibial plateau plays a major role in determining the plays a major role in determining the Maintains shape and distributes forces in the knee biomechanical properties of collagen in tissue. biomechanical properties of collagen in tissue. The straightening of the crimp allows tendons The straightening of the crimp allows tendons and ligaments to absorb and distribute forces and ligaments to absorb and distribute forces gradually, helping to prevent injury. gradually, helping to prevent injury. Elastin